1. Field of the Invention
The present invention relates to a diamond rectifying element comprising a pair of electrodes provided on the surface of semiconducting diamond film or provided so as to sandwich said semiconducting diamond film, more particularly to a diamond rectifying element suitable for use under high temperature.
2. Prior Art
Diamond has a large band gap (5.5 eV) as well as a high thermal conductivity (20 W.K/cm) and high carrier mobilities (2000 cm.sup.2 /V.sec. for electron and 2100 cm.sup.2 /V.sec. for hole) and a high dielectric breakdown voltage (10.sup.7 V/cm). Since it is possible to make a diamond semiconductor by incorporating appropriate impurity atoms in the diamond film, the film has drawn a considerable attention for application to various fields such as electronic devices working under high temperature and radiation, and high power and high frequency devices.
In addition, there are many proposals for various structures and manufacturing processes for rectifying elements using diamond films (Japanese under Provisional Publications hei 3-120865, 3-278474, 4-26161, 3-278463, 1-244399, and FP 1589, and U.S. Pat. No. 5,086,014).
Diamond rectifying elements according to these prior art all comprises a single crystal diamond substrate, a homoepitaxial diamond film, or a polycrystalline diamond film. Single crystal diamond has a disadvantage for practical use of rectifying element due to its small surface area (several square mm). Moreover, single crystal diamond is very expensive so that the manufacturing cost will also be high. Further, many crystal defects are contained in natural and synthetic single crystal diamonds, therefore the electrical characteristics of the rectifying elements have not reached to the level of theoretical characteristics for single crystal diamond.
Recent advancement of diamond film deposition technology has made possible to grow uniform polycrystalline diamond film on a large non-diamond substrate. Production of rectifying elements using polycrystalline diamond films has an advantage that many rectifying elements can be fabricated simultaneously and hence the manufacturing cost can be reduced. However, currently produced polycrystalline diamond films contain many grain boundaries and crystal defects, and the film surface is very rough. The grain boundaries cause carrier scatterings, which results in a significant reduction of the carrier mobilities as well as unwanted current leakages. If the element is used at high temperature in air, the diamond film is gradually oxidized and graphitized along grain boundaries. Therefore, the maximum operation temperature of the rectifying element is restricted compared with homoepitaxial film elements. Crystal defects also are responsible to current leakages in the reversed bias state. The roughness of the film surface causes a nonuniform electric field, leading to dielectric breakdown at low voltage.
Thus, although polycrystalline diamond films have an advantage for the mass production of rectifying elements the characteristics of the rectifying elements are still far from the commercially acceptable level.